The Three Stigmata of Palmer Eldritch by Philip K Dick

In the overcrowded world and cramped space colonies of the late twenty-first century, tedium can be endured through the use of the drug Can-D, which enables the user to inhabit a shared illusory world.

But when industrialist Palmer Eldritch returns from an interstellar trip, he brings with him a new drug, Chew-Z, which is far more potent than Can-D. But could the permanent state of drugged illusion it induces be part of something much more sinister?